Spoiler Dark Interlopers Sheika?

[Lambsquirt]

Ever wonder why theres a triforce on the mirror of twilight? It clearly uses twili magic. We only know that the sages used this mirror to seal the interlopers away so I see 2 possibilities

The interlopers made the mirror and the sages took it from them

The sages used the fused shadows that they took from the interlopers to make the mirror

If the interlopers did indeed make it, then perhaps that serves as evidence that it was the sheikah. We know the interlopers wanted the triforce but that doesmt really seem like a real reason to brand it on your magic mirror.
I theorize that the sheikah rebeled from the royal family, and felt entitled to the triforce. They thougjt the hylians couldnt handle the triforce anymore and tried to claim it for themselves, but the hylians won, and the sages sealed the sheikah away with their own magic.

Its also worth noting that the sheikah and twili are both closely associated with shadows.

#Facts the Shadow temple and Bongo-Bongo give this validity.
Without a doubt there was a dark sect of the Sheika.